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zstd/contrib/long_distance_matching/ldm.c

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#include <limits.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "ldm.h"
#define LDM_HASHTABLESIZE (1 << (LDM_MEMORY_USAGE))
#define LDM_HASHTABLESIZE_U32 ((LDM_HASHTABLESIZE) >> 2)
#define LDM_HASHTABLESIZE_U64 ((LDM_HASHTABLESIZE) >> 3)
#if USE_CHECKSUM
#define LDM_HASH_ENTRY_SIZE_LOG 3
#else
#define LDM_HASH_ENTRY_SIZE_LOG 2
#endif
// Entries are inserted into the table HASH_ONLY_EVERY + 1 times "on average".
#ifndef HASH_ONLY_EVERY_LOG
#define HASH_ONLY_EVERY_LOG (LDM_WINDOW_SIZE_LOG-((LDM_MEMORY_USAGE)-(LDM_HASH_ENTRY_SIZE_LOG)))
#endif
#define HASH_ONLY_EVERY ((1 << (HASH_ONLY_EVERY_LOG)) - 1)
#define HASH_BUCKET_SIZE (1 << (HASH_BUCKET_SIZE_LOG))
#define NUM_HASH_BUCKETS_LOG ((LDM_MEMORY_USAGE)-(LDM_HASH_ENTRY_SIZE_LOG)-(HASH_BUCKET_SIZE_LOG))
#define HASH_CHAR_OFFSET 10
// Take the first match in the hash bucket only.
//#define ZSTD_SKIP
static const U64 prime8bytes = 11400714785074694791ULL;
// Type of the small hash used to index into the hash table.
typedef U32 hash_t;
#if USE_CHECKSUM
typedef struct LDM_hashEntry {
U32 offset;
U32 checksum;
} LDM_hashEntry;
#else
typedef struct LDM_hashEntry {
U32 offset;
} LDM_hashEntry;
#endif
struct LDM_compressStats {
U32 windowSizeLog, hashTableSizeLog;
U32 numMatches;
U64 totalMatchLength;
U64 totalLiteralLength;
U64 totalOffset;
U32 matchLengthHistogram[32];
U32 minOffset, maxOffset;
U32 offsetHistogram[32];
};
typedef struct LDM_hashTable LDM_hashTable;
struct LDM_CCtx {
size_t isize; /* Input size */
size_t maxOSize; /* Maximum output size */
const BYTE *ibase; /* Base of input */
const BYTE *ip; /* Current input position */
const BYTE *iend; /* End of input */
// Maximum input position such that hashing at the position does not exceed
// end of input.
const BYTE *ihashLimit;
// Maximum input position such that finding a match of at least the minimum
// match length does not exceed end of input.
const BYTE *imatchLimit;
const BYTE *obase; /* Base of output */
BYTE *op; /* Output */
const BYTE *anchor; /* Anchor to start of current (match) block */
LDM_compressStats stats; /* Compression statistics */
LDM_hashTable *hashTable;
const BYTE *lastPosHashed; /* Last position hashed */
U64 lastHash;
const BYTE *nextIp; // TODO: this is redundant (ip + step)
const BYTE *nextPosHashed;
U64 nextHash;
unsigned step; // ip step, should be 1.
const BYTE *lagIp;
U64 lagHash;
};
struct LDM_hashTable {
U32 numBuckets; // The number of buckets.
U32 numEntries; // numBuckets * HASH_BUCKET_SIZE.
LDM_hashEntry *entries;
BYTE *bucketOffsets; // A pointer (per bucket) to the next insert position.
};
static void HASH_destroyTable(LDM_hashTable *table) {
free(table->entries);
free(table->bucketOffsets);
free(table);
}
/**
* Create a hash table that can contain size elements.
* The number of buckets is determined by size >> HASH_BUCKET_SIZE_LOG.
*
* Returns NULL if table creation failed.
*/
static LDM_hashTable *HASH_createTable(U32 size) {
LDM_hashTable *table = malloc(sizeof(LDM_hashTable));
if (!table) return NULL;
table->numBuckets = size >> HASH_BUCKET_SIZE_LOG;
table->numEntries = size;
table->entries = calloc(size, sizeof(LDM_hashEntry));
table->bucketOffsets = calloc(size >> HASH_BUCKET_SIZE_LOG, sizeof(BYTE));
if (!table->entries || !table->bucketOffsets) {
HASH_destroyTable(table);
return NULL;
}
return table;
}
static LDM_hashEntry *getBucket(const LDM_hashTable *table, const hash_t hash) {
return table->entries + (hash << HASH_BUCKET_SIZE_LOG);
}
static unsigned ZSTD_NbCommonBytes (register size_t val) {
if (MEM_isLittleEndian()) {
if (MEM_64bits()) {
# if defined(_MSC_VER) && defined(_WIN64)
unsigned long r = 0;
_BitScanForward64( &r, (U64)val );
return (unsigned)(r>>3);
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_ctzll((U64)val) >> 3);
# else
static const int DeBruijnBytePos[64] = { 0, 0, 0, 0, 0, 1, 1, 2,
0, 3, 1, 3, 1, 4, 2, 7,
0, 2, 3, 6, 1, 5, 3, 5,
1, 3, 4, 4, 2, 5, 6, 7,
7, 0, 1, 2, 3, 3, 4, 6,
2, 6, 5, 5, 3, 4, 5, 6,
7, 1, 2, 4, 6, 4, 4, 5,
7, 2, 6, 5, 7, 6, 7, 7 };
return DeBruijnBytePos[
((U64)((val & -(long long)val) * 0x0218A392CDABBD3FULL)) >> 58];
# endif
} else { /* 32 bits */
# if defined(_MSC_VER)
unsigned long r=0;
_BitScanForward( &r, (U32)val );
return (unsigned)(r>>3);
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_ctz((U32)val) >> 3);
# else
static const int DeBruijnBytePos[32] = { 0, 0, 3, 0, 3, 1, 3, 0,
3, 2, 2, 1, 3, 2, 0, 1,
3, 3, 1, 2, 2, 2, 2, 0,
3, 1, 2, 0, 1, 0, 1, 1 };
return DeBruijnBytePos[
((U32)((val & -(S32)val) * 0x077CB531U)) >> 27];
# endif
}
} else { /* Big Endian CPU */
if (MEM_64bits()) {
# if defined(_MSC_VER) && defined(_WIN64)
unsigned long r = 0;
_BitScanReverse64( &r, val );
return (unsigned)(r>>3);
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_clzll(val) >> 3);
# else
unsigned r;
/* calculate this way due to compiler complaining in 32-bits mode */
const unsigned n32 = sizeof(size_t)*4;
if (!(val>>n32)) { r=4; } else { r=0; val>>=n32; }
if (!(val>>16)) { r+=2; val>>=8; } else { val>>=24; }
r += (!val);
return r;
# endif
} else { /* 32 bits */
# if defined(_MSC_VER)
unsigned long r = 0;
_BitScanReverse( &r, (unsigned long)val );
return (unsigned)(r>>3);
# elif defined(__GNUC__) && (__GNUC__ >= 3)
return (__builtin_clz((U32)val) >> 3);
# else
unsigned r;
if (!(val>>16)) { r=2; val>>=8; } else { r=0; val>>=24; }
r += (!val);
return r;
# endif
}
}
}
// From lib/compress/zstd_compress.c
static size_t ZSTD_count(const BYTE *pIn, const BYTE *pMatch,
const BYTE *const pInLimit) {
const BYTE * const pStart = pIn;
const BYTE * const pInLoopLimit = pInLimit - (sizeof(size_t)-1);
while (pIn < pInLoopLimit) {
size_t const diff = MEM_readST(pMatch) ^ MEM_readST(pIn);
if (!diff) {
pIn += sizeof(size_t);
pMatch += sizeof(size_t);
continue;
}
pIn += ZSTD_NbCommonBytes(diff);
return (size_t)(pIn - pStart);
}
if (MEM_64bits()) {
if ((pIn < (pInLimit - 3)) && (MEM_read32(pMatch) == MEM_read32(pIn))) {
pIn += 4;
pMatch += 4;
}
}
if ((pIn < (pInLimit - 1)) && (MEM_read16(pMatch) == MEM_read16(pIn))) {
pIn += 2;
pMatch += 2;
}
if ((pIn < pInLimit) && (*pMatch == *pIn)) {
pIn++;
}
return (size_t)(pIn - pStart);
}
/**
* Count number of bytes that match backwards before pIn and pMatch.
*
* We count only bytes where pMatch > pBase and pIn > pAnchor.
*/
static size_t countBackwardsMatch(const BYTE *pIn, const BYTE *pAnchor,
const BYTE *pMatch, const BYTE *pBase) {
size_t matchLength = 0;
while (pIn > pAnchor && pMatch > pBase && pIn[-1] == pMatch[-1]) {
pIn--;
pMatch--;
matchLength++;
}
return matchLength;
}
/**
* Returns a pointer to the entry in the hash table matching the hash and
* checksum with the "longest match length" as defined below. The forward and
* backward match lengths are written to *pForwardMatchLength and
* *pBackwardMatchLength.
*
* The match length is defined based on cctx->ip and the entry's offset.
* The forward match is computed from cctx->ip and entry->offset + cctx->ibase.
* The backward match is computed backwards from cctx->ip and
* cctx->ibase only if the forward match is longer than LDM_MIN_MATCH_LENGTH.
*/
static LDM_hashEntry *HASH_getBestEntry(const LDM_CCtx *cctx,
const hash_t hash,
const U32 checksum,
U64 *pForwardMatchLength,
U64 *pBackwardMatchLength) {
LDM_hashTable *table = cctx->hashTable;
LDM_hashEntry *bucket = getBucket(table, hash);
LDM_hashEntry *cur;
LDM_hashEntry *bestEntry = NULL;
U64 bestMatchLength = 0;
#if !(USE_CHECKSUM)
(void)checksum;
#endif
for (cur = bucket; cur < bucket + HASH_BUCKET_SIZE; ++cur) {
const BYTE *pMatch = cur->offset + cctx->ibase;
// Check checksum for faster check.
#if USE_CHECKSUM
if (cur->checksum == checksum &&
cctx->ip - pMatch <= LDM_WINDOW_SIZE) {
#else
if (cctx->ip - pMatch <= LDM_WINDOW_SIZE) {
#endif
U64 forwardMatchLength = ZSTD_count(cctx->ip, pMatch, cctx->iend);
U64 backwardMatchLength, totalMatchLength;
// Only take matches where the forward match length is large enough
// for speed.
if (forwardMatchLength < LDM_MIN_MATCH_LENGTH) {
continue;
}
backwardMatchLength =
countBackwardsMatch(cctx->ip, cctx->anchor,
cur->offset + cctx->ibase,
cctx->ibase);
totalMatchLength = forwardMatchLength + backwardMatchLength;
if (totalMatchLength >= bestMatchLength) {
bestMatchLength = totalMatchLength;
*pForwardMatchLength = forwardMatchLength;
*pBackwardMatchLength = backwardMatchLength;
bestEntry = cur;
#ifdef ZSTD_SKIP
return cur;
#endif
}
}
}
if (bestEntry != NULL) {
return bestEntry;
}
return NULL;
}
/**
* Insert an entry into the hash table. The table uses a "circular buffer",
* with the oldest entry overwritten.
*/
static void HASH_insert(LDM_hashTable *table,
const hash_t hash, const LDM_hashEntry entry) {
*(getBucket(table, hash) + table->bucketOffsets[hash]) = entry;
table->bucketOffsets[hash]++;
table->bucketOffsets[hash] &= HASH_BUCKET_SIZE - 1;
}
static void HASH_outputTableOccupancy(const LDM_hashTable *table) {
U32 ctr = 0;
LDM_hashEntry *cur = table->entries;
LDM_hashEntry *end = table->entries + (table->numBuckets * HASH_BUCKET_SIZE);
for (; cur < end; ++cur) {
if (cur->offset == 0) {
ctr++;
}
}
// The number of buckets is repeated as a check for now.
printf("Num buckets, bucket size: %d (2^%d), %d\n",
table->numBuckets, NUM_HASH_BUCKETS_LOG, HASH_BUCKET_SIZE);
printf("Hash table size, empty slots, %% empty: %u, %u, %.3f\n",
table->numEntries, ctr,
100.0 * (double)(ctr) / table->numEntries);
}
// TODO: This can be done more efficiently, for example by using builtin
// functions (but it is not that important as it is only used for computing
// stats).
static int intLog2(U64 x) {
int ret = 0;
while (x >>= 1) {
ret++;
}
return ret;
}
void LDM_printCompressStats(const LDM_compressStats *stats) {
printf("=====================\n");
printf("Compression statistics\n");
printf("Window size, hash table size (bytes): 2^%u, 2^%u\n",
stats->windowSizeLog, stats->hashTableSizeLog);
printf("num matches, total match length, %% matched: %u, %llu, %.3f\n",
stats->numMatches,
stats->totalMatchLength,
100.0 * (double)stats->totalMatchLength /
(double)(stats->totalMatchLength + stats->totalLiteralLength));
printf("avg match length: %.1f\n", ((double)stats->totalMatchLength) /
(double)stats->numMatches);
printf("avg literal length, total literalLength: %.1f, %llu\n",
((double)stats->totalLiteralLength) / (double)stats->numMatches,
stats->totalLiteralLength);
printf("avg offset length: %.1f\n",
((double)stats->totalOffset) / (double)stats->numMatches);
printf("min offset, max offset: %u, %u\n",
stats->minOffset, stats->maxOffset);
printf("\n");
printf("offset histogram | match length histogram\n");
printf("offset/ML, num matches, %% of matches | num matches, %% of matches\n");
{
int i;
int logMaxOffset = intLog2(stats->maxOffset);
for (i = 0; i <= logMaxOffset; i++) {
printf("2^%*d: %10u %6.3f%% |2^%*d: %10u %6.3f \n",
2, i,
stats->offsetHistogram[i],
100.0 * (double) stats->offsetHistogram[i] /
(double) stats->numMatches,
2, i,
stats->matchLengthHistogram[i],
100.0 * (double) stats->matchLengthHistogram[i] /
(double) stats->numMatches);
}
}
printf("\n");
printf("=====================\n");
}
/**
* Return the upper (most significant) NUM_HASH_BUCKETS_LOG bits.
*/
static hash_t getSmallHash(U64 hash) {
return hash >> (64 - NUM_HASH_BUCKETS_LOG);
}
/**
* Return the 32 bits after the upper NUM_HASH_BUCKETS_LOG bits.
*/
static U32 getChecksum(U64 hash) {
return (hash >> (64 - 32 - NUM_HASH_BUCKETS_LOG)) & 0xFFFFFFFF;
}
#if INSERT_BY_TAG
static U32 lowerBitsFromHfHash(U64 hash) {
// The number of bits used so far is NUM_HASH_BUCKETS_LOG + 32.
// So there are 32 - NUM_HASH_BUCKETS_LOG bits left.
// Occasional hashing requires HASH_ONLY_EVERY_LOG bits.
// So if 32 - LDMHASHLOG < HASH_ONLY_EVERY_LOG, just return lower bits
// allowing for reuse of bits.
if (32 - NUM_HASH_BUCKETS_LOG < HASH_ONLY_EVERY_LOG) {
return hash & HASH_ONLY_EVERY;
} else {
// Otherwise shift by
// (32 - NUM_HASH_BUCKETS_LOG - HASH_ONLY_EVERY_LOG) bits first.
return (hash >> (32 - NUM_HASH_BUCKETS_LOG - HASH_ONLY_EVERY_LOG)) &
HASH_ONLY_EVERY;
}
}
#endif
/**
* Get a 64-bit hash using the first len bytes from buf.
*
* Giving bytes s = s_1, s_2, ... s_k, the hash is defined to be
* H(s) = s_1*(a^(k-1)) + s_2*(a^(k-2)) + ... + s_k*(a^0)
*
* where the constant a is defined to be prime8bytes.
*
* The implementation adds an offset to each byte, so
* H(s) = (s_1 + HASH_CHAR_OFFSET)*(a^(k-1)) + ...
*/
static U64 getHash(const BYTE *buf, U32 len) {
U64 ret = 0;
U32 i;
for (i = 0; i < len; i++) {
ret *= prime8bytes;
ret += buf[i] + HASH_CHAR_OFFSET;
}
return ret;
}
static U64 ipow(U64 base, U64 exp) {
U64 ret = 1;
while (exp) {
if (exp & 1) {
ret *= base;
}
exp >>= 1;
base *= base;
}
return ret;
}
static U64 updateHash(U64 hash, U32 len,
BYTE toRemove, BYTE toAdd) {
// TODO: this relies on compiler optimization.
// The exponential can be calculated explicitly as len is constant.
hash -= ((toRemove + HASH_CHAR_OFFSET) *
ipow(prime8bytes, len - 1));
hash *= prime8bytes;
hash += toAdd + HASH_CHAR_OFFSET;
return hash;
}
/**
* Update cctx->nextHash and cctx->nextPosHashed
* based on cctx->lastHash and cctx->lastPosHashed.
*
* This uses a rolling hash and requires that the last position hashed
* corresponds to cctx->nextIp - step.
*/
static void setNextHash(LDM_CCtx *cctx) {
cctx->nextHash = updateHash(
cctx->lastHash, LDM_HASH_LENGTH,
cctx->lastPosHashed[0],
cctx->lastPosHashed[LDM_HASH_LENGTH]);
cctx->nextPosHashed = cctx->nextIp;
#if LDM_LAG
if (cctx->ip - cctx->ibase > LDM_LAG) {
cctx->lagHash = updateHash(
cctx->lagHash, LDM_HASH_LENGTH,
cctx->lagIp[0], cctx->lagIp[LDM_HASH_LENGTH]);
cctx->lagIp++;
}
#endif
}
static void putHashOfCurrentPositionFromHash(LDM_CCtx *cctx, U64 hash) {
// Hash only every HASH_ONLY_EVERY times, based on cctx->ip.
// Note: this works only when cctx->step is 1.
#if LDM_LAG
if (cctx -> lagIp - cctx->ibase > 0) {
#if INSERT_BY_TAG
U32 hashEveryMask = lowerBitsFromHfHash(cctx->lagHash);
if (hashEveryMask == HASH_ONLY_EVERY) {
#else
if (((cctx->ip - cctx->ibase) & HASH_ONLY_EVERY) == HASH_ONLY_EVERY) {
#endif
U32 smallHash = getSmallHash(cctx->lagHash);
# if USE_CHECKSUM
U32 checksum = getChecksum(cctx->lagHash);
const LDM_hashEntry entry = { cctx->lagIp - cctx->ibase, checksum };
# else
const LDM_hashEntry entry = { cctx->lagIp - cctx->ibase };
# endif
HASH_insert(cctx->hashTable, smallHash, entry);
}
} else {
#endif // LDM_LAG
#if INSERT_BY_TAG
U32 hashEveryMask = lowerBitsFromHfHash(hash);
if (hashEveryMask == HASH_ONLY_EVERY) {
#else
if (((cctx->ip - cctx->ibase) & HASH_ONLY_EVERY) == HASH_ONLY_EVERY) {
#endif
U32 smallHash = getSmallHash(hash);
#if USE_CHECKSUM
U32 checksum = getChecksum(hash);
const LDM_hashEntry entry = { cctx->ip - cctx->ibase, checksum };
#else
const LDM_hashEntry entry = { cctx->ip - cctx->ibase };
#endif
HASH_insert(cctx->hashTable, smallHash, entry);
}
#if LDM_LAG
}
#endif
cctx->lastPosHashed = cctx->ip;
cctx->lastHash = hash;
}
/**
* Copy over the cctx->lastHash, and cctx->lastPosHashed
* fields from the "next" fields.
*
* This requires that cctx->ip == cctx->nextPosHashed.
*/
static void LDM_updateLastHashFromNextHash(LDM_CCtx *cctx) {
putHashOfCurrentPositionFromHash(cctx, cctx->nextHash);
}
/**
* Insert hash of the current position into the hash table.
*/
static void LDM_putHashOfCurrentPosition(LDM_CCtx *cctx) {
U64 hash = getHash(cctx->ip, LDM_HASH_LENGTH);
putHashOfCurrentPositionFromHash(cctx, hash);
}
size_t LDM_initializeCCtx(LDM_CCtx *cctx,
const void *src, size_t srcSize,
void *dst, size_t maxDstSize) {
cctx->isize = srcSize;
cctx->maxOSize = maxDstSize;
cctx->ibase = (const BYTE *)src;
cctx->ip = cctx->ibase;
cctx->iend = cctx->ibase + srcSize;
cctx->ihashLimit = cctx->iend - LDM_HASH_LENGTH;
cctx->imatchLimit = cctx->iend - LDM_MIN_MATCH_LENGTH;
cctx->obase = (BYTE *)dst;
cctx->op = (BYTE *)dst;
cctx->anchor = cctx->ibase;
memset(&(cctx->stats), 0, sizeof(cctx->stats));
#if USE_CHECKSUM
cctx->hashTable = HASH_createTable(LDM_HASHTABLESIZE_U64);
#else
cctx->hashTable = HASH_createTable(LDM_HASHTABLESIZE_U32);
#endif
if (!cctx->hashTable) return 1;
cctx->stats.minOffset = UINT_MAX;
cctx->stats.windowSizeLog = LDM_WINDOW_SIZE_LOG;
cctx->stats.hashTableSizeLog = LDM_MEMORY_USAGE;
cctx->lastPosHashed = NULL;
cctx->step = 1; // Fixed to be 1 for now. Changing may break things.
cctx->nextIp = cctx->ip + cctx->step;
cctx->nextPosHashed = 0;
return 0;
}
void LDM_destroyCCtx(LDM_CCtx *cctx) {
HASH_destroyTable(cctx->hashTable);
}
/**
* Finds the "best" match.
*
* Returns 0 if successful and 1 otherwise (i.e. no match can be found
* in the remaining input that is long enough).
*
* forwardMatchLength contains the forward length of the match.
*/
static int LDM_findBestMatch(LDM_CCtx *cctx, const BYTE **match,
U64 *forwardMatchLength, U64 *backwardMatchLength) {
LDM_hashEntry *entry = NULL;
cctx->nextIp = cctx->ip + cctx->step;
while (entry == NULL) {
U64 hash;
hash_t smallHash;
U32 checksum;
#if INSERT_BY_TAG
U32 hashEveryMask;
#endif
setNextHash(cctx);
hash = cctx->nextHash;
smallHash = getSmallHash(hash);
checksum = getChecksum(hash);
#if INSERT_BY_TAG
hashEveryMask = lowerBitsFromHfHash(hash);
#endif
cctx->ip = cctx->nextIp;
cctx->nextIp += cctx->step;
if (cctx->ip > cctx->imatchLimit) {
return 1;
}
#if INSERT_BY_TAG
if (hashEveryMask == HASH_ONLY_EVERY) {
entry = HASH_getBestEntry(cctx, smallHash, checksum,
forwardMatchLength, backwardMatchLength);
}
#else
entry = HASH_getBestEntry(cctx, smallHash, checksum,
forwardMatchLength, backwardMatchLength);
#endif
if (entry != NULL) {
*match = entry->offset + cctx->ibase;
}
putHashOfCurrentPositionFromHash(cctx, hash);
}
setNextHash(cctx);
return 0;
}
void LDM_encodeLiteralLengthAndLiterals(
LDM_CCtx *cctx, BYTE *pToken, const U64 literalLength) {
/* Encode the literal length. */
if (literalLength >= RUN_MASK) {
U64 len = (U64)literalLength - RUN_MASK;
*pToken = (RUN_MASK << ML_BITS);
for (; len >= 255; len -= 255) {
*(cctx->op)++ = 255;
}
*(cctx->op)++ = (BYTE)len;
} else {
*pToken = (BYTE)(literalLength << ML_BITS);
}
/* Encode the literals. */
memcpy(cctx->op, cctx->anchor, literalLength);
cctx->op += literalLength;
}
void LDM_outputBlock(LDM_CCtx *cctx,
const U64 literalLength,
const U32 offset,
const U64 matchLength) {
BYTE *pToken = cctx->op++;
/* Encode the literal length and literals. */
LDM_encodeLiteralLengthAndLiterals(cctx, pToken, literalLength);
/* Encode the offset. */
MEM_write32(cctx->op, offset);
cctx->op += LDM_OFFSET_SIZE;
/* Encode the match length. */
if (matchLength >= ML_MASK) {
U64 matchLengthRemaining = matchLength;
*pToken += ML_MASK;
matchLengthRemaining -= ML_MASK;
MEM_write32(cctx->op, 0xFFFFFFFF);
while (matchLengthRemaining >= 4*0xFF) {
cctx->op += 4;
MEM_write32(cctx->op, 0xffffffff);
matchLengthRemaining -= 4*0xFF;
}
cctx->op += matchLengthRemaining / 255;
*(cctx->op)++ = (BYTE)(matchLengthRemaining % 255);
} else {
*pToken += (BYTE)(matchLength);
}
}
// TODO: maxDstSize is unused. This function may seg fault when writing
// beyond the size of dst, as it does not check maxDstSize. Writing to
// a buffer and performing checks is a possible solution.
//
// This is based upon lz4.
size_t LDM_compress(const void *src, size_t srcSize,
void *dst, size_t maxDstSize) {
LDM_CCtx cctx;
const BYTE *match = NULL;
U64 forwardMatchLength = 0;
U64 backwardsMatchLength = 0;
if (LDM_initializeCCtx(&cctx, src, srcSize, dst, maxDstSize)) {
// Initialization failed.
return 0;
}
#ifdef OUTPUT_CONFIGURATION
LDM_outputConfiguration();
#endif
/* Hash the first position and put it into the hash table. */
LDM_putHashOfCurrentPosition(&cctx);
cctx.lagIp = cctx.ip;
cctx.lagHash = cctx.lastHash;
/**
* Find a match.
* If no more matches can be found (i.e. the length of the remaining input
* is less than the minimum match length), then stop searching for matches
* and encode the final literals.
*/
while (!LDM_findBestMatch(&cctx, &match, &forwardMatchLength,
&backwardsMatchLength)) {
#ifdef COMPUTE_STATS
cctx.stats.numMatches++;
#endif
cctx.ip -= backwardsMatchLength;
match -= backwardsMatchLength;
/**
* Write current block (literals, literal length, match offset, match
* length) and update pointers and hashes.
*/
{
const U64 literalLength = cctx.ip - cctx.anchor;
const U32 offset = cctx.ip - match;
const U64 matchLength = forwardMatchLength +
backwardsMatchLength -
LDM_MIN_MATCH_LENGTH;
LDM_outputBlock(&cctx, literalLength, offset, matchLength);
#ifdef COMPUTE_STATS
cctx.stats.totalLiteralLength += literalLength;
cctx.stats.totalOffset += offset;
cctx.stats.totalMatchLength += matchLength + LDM_MIN_MATCH_LENGTH;
cctx.stats.minOffset =
offset < cctx.stats.minOffset ? offset : cctx.stats.minOffset;
cctx.stats.maxOffset =
offset > cctx.stats.maxOffset ? offset : cctx.stats.maxOffset;
cctx.stats.offsetHistogram[(U32)intLog2(offset)]++;
cctx.stats.matchLengthHistogram[
(U32)intLog2(matchLength + LDM_MIN_MATCH_LENGTH)]++;
#endif
// Move ip to end of block, inserting hashes at each position.
cctx.nextIp = cctx.ip + cctx.step;
while (cctx.ip < cctx.anchor + LDM_MIN_MATCH_LENGTH +
matchLength + literalLength) {
if (cctx.ip > cctx.lastPosHashed) {
// TODO: Simplify.
LDM_updateLastHashFromNextHash(&cctx);
setNextHash(&cctx);
}
cctx.ip++;
cctx.nextIp++;
}
}
// Set start of next block to current input pointer.
cctx.anchor = cctx.ip;
LDM_updateLastHashFromNextHash(&cctx);
}
/* Encode the last literals (no more matches). */
{
const U64 lastRun = cctx.iend - cctx.anchor;
BYTE *pToken = cctx.op++;
LDM_encodeLiteralLengthAndLiterals(&cctx, pToken, lastRun);
}
#ifdef COMPUTE_STATS
LDM_printCompressStats(&cctx.stats);
HASH_outputTableOccupancy(cctx.hashTable);
#endif
{
const size_t ret = cctx.op - cctx.obase;
LDM_destroyCCtx(&cctx);
return ret;
}
}
void LDM_outputConfiguration(void) {
printf("=====================\n");
printf("Configuration\n");
printf("LDM_WINDOW_SIZE_LOG: %d\n", LDM_WINDOW_SIZE_LOG);
printf("LDM_MIN_MATCH_LENGTH, LDM_HASH_LENGTH: %d, %d\n",
LDM_MIN_MATCH_LENGTH, LDM_HASH_LENGTH);
printf("LDM_MEMORY_USAGE: %d\n", LDM_MEMORY_USAGE);
printf("HASH_ONLY_EVERY_LOG: %d\n", HASH_ONLY_EVERY_LOG);
printf("HASH_BUCKET_SIZE_LOG: %d\n", HASH_BUCKET_SIZE_LOG);
printf("LDM_LAG: %d\n", LDM_LAG);
printf("USE_CHECKSUM: %d\n", USE_CHECKSUM);
printf("INSERT_BY_TAG: %d\n", INSERT_BY_TAG);
printf("HASH_CHAR_OFFSET: %d\n", HASH_CHAR_OFFSET);
printf("=====================\n");
}
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